1. Field of the Invention
The present invention relates to a photosensitive unit, a light source, and an image forming apparatus for use in a copying machine, a printer and a facsimile.
2. Description of the Related Art
Known, as a conventional image forming process, is an electrophotography. A representative example is a Carlson process or xerography. According to xerography, a resinous powder forms on an electrically charged plate an image, and this image is transferred and thermally fixed onto a paper. This image recording technique requires six processes, which include charging, exposing, developing, transferring, fixing, and cleaning. Each of such processes requires its own unit, resulting in a bulky machine.
U.S. Pat. No. 5,815,774 (=JP-A 9-204092) issued to Funayama et al. discloses a simplified process alternative to the Carlson process. This simplified process uses a porous photosensitive unit (PPU). The PPU includes a transparent substrate, a transparent conductive layer formed over the substrate, and a photoconductive layer formed over the transparent conductive layer. The PPU also includes a porous insulating layer formed over the photoconductive layer. The porous insulating layer has a screen or an upper electrode formed over the surface thereof. Conductive color particles that are charged to one polarity are attracted to the PPU to fill holes of the porous insulating layer. Subsequently, when a light corresponding to an image is irradiated to the photoconductive layer of the PPU, the color particles within an area exposed to the light are charged to the opposite polarity. These color particles are transferred to a recording medium, forming the image thereon.
Referring to FIG. 13, a description is made on the image recording technique disclosed in the above-mentioned U.S. Pat. No. 5,815,774. FIG. 13 illustrates the principle of the image recording technique.
The image recording technique requires processes, which include color particles filling, exposing and transferring, and fixing. Hereinafter, a description is made on the exposing and transferring process.
In FIG. 13, the reference numeral 11 generally designates holes of a porous insulating layer 4 of a PPU 10, namely, first, second and third holes 11a, 11b, and 11c. As illustrated, the minute holes 11a, 11b, and 11c are filled with conductive color particles that have been fed thereto during color particles filling process.
A light source illuminates in a pattern corresponding to data to be printed. Light 9 from the light source passes through a transparent substrate 1 and a transparent conductive layer 2 to reach a photoconductive layer 3, exposing a region 7, called "exposed region, " of the photoconductive layer 3 in the pattern corresponding to the data to be printed. Electric charges are induced within the exposed region 7, only. An upper electrode 5 above the porous insulating layer 4 is held at a predetermined negative potential for attracting positive electric charges 8 induced by the light irradiation. Thus, among the electric charges inducted by the light irradiation, positive electric charges move toward the surface of the photoconductive layer 3 for injection into the negatively charged color particles 6 that are received in the holes 11. The negatively charged color particles 6 are neutralized and then positively charged. The transparent conductive layer 2 is held at a predetermined positive potential to neutralize the negatively charged particles that have been induced due to the light irradiation. As a result, an electric repulsion force is generated between the positively charged color particles 6 and the transparent conductive layer 2, causing the color particles 6 to fly out of the holes 11. The color particles 6 that have flown are attached by adhesion to a recording medium to form an image of the data to be printed. This image is fixed during the subsequent fixing process.
According to the image recording technique, color particles filling process, exposing and transferring process, and fixing process complete an image recording. Making it possible to construct a compact machine. Since a light source as used in ordinary electrophotography may be used, the conventional technology is advantageous in cost.